You're missing the point. The poster made a very poor analogy.
But I have also previously linked to a speaker video that is very well recorded, and does indeed give a good feel for the quality of the component. Of course a fair comparison would require that both components are equally well recorded, etc. But it absolutely is possible to glean valuable insights from such videos.
Would I suggest buying on that basis alone? Of course not! But for that matter, it can even be treacherous to purchase on the basis of an in-person audition at a dealer, as the room and or associated components may produce a very different sound.